For charging energy accumulators in motor vehicles, for example in the form of traction batteries such as those in hybrid or electric vehicles, besides external charging units on-board charging units are also used, which advantageously make use of the specific on-board infrastructure of the electric drive-train.
The document DE 693 03 150 T2 discloses a system in which a selectively switchable main voltage source charges an energy accumulator by way of a rotating field machine and a rectifier. The document EP 0 834 977 A2 in addition discloses a charging device in which the inductances of the electric machine can advantageously be used to form a step-up converter for setting the charging voltage.